The present invention relates to the field of medicine, and more particularly to the field of intracorporeal devices such as stents. The present invention also relates to the field of expandable intraluminal support devices such as stents and the like.
Typically, stents are expandable, tubular metallic devices that are positioned within a patient's vasculature or other body lumen and expanded in order to support a vessel or body lumen and allow the flow of blood or other body fluids therethrough. Often, the stents are formed from a deformable metal and delivered to a desired intraluminal location using a balloon-type catheter. By advancing the catheter through the body lumen, the stent may be delivered to a desired position. Inflating the balloon then deforms the stent into an expanded configuration, seating it within the artery or other body lumen. Other implementations make use of a self-expanding stent formed from a suitable material such as pseudoelastic material that is delivered in a constricted condition and when released spontaneously expands to an enlarged configuration. In other embodiments, a stent made of shape memory alloy (e.g. NiTi alloy) is inserted into the body lumen in a martensitic phase and transforms to an austenite phase which has an expanded memory when raised to a temperature above the transformation temperature, usually less than 45° C.
Stents are often used in conjunction with an intravascular treatment for obstructive coronary artery disease. For example, ablation, atherectomy, balloon dilation, laser treatment or other procedures are among the method used to widen a stenotic region of a patient's vasculature. However, restenosis occurs in large percentage of percutaneous transluminal coronary angioplasty (PTCA) patients and rates can be even higher with other procedures. The prior art has employed a number of mechanical and pharmacological strategies to reduce the restenosis rate, but none have been particularly effective. Accordingly, stents have been proposed to maintain the patency of a treated vessel and prevent restenosis. Using stents, restenosis rates have fallen to less than 20%.
Restenosis is thought to be a natural healing reaction provoked by injury from the intravascular procedure. The healing process frequently causes thrombosis and may lead to intimal hyperplasia that occludes the vessel. Although helpful in reducing restenosis, stents do not represent a complete solution. The framework of the stent may still allow migration and proliferation of the smooth muscle cells, while the stent itself can be thrombogenic. To address these problems, stents have been covered with DACRON, PTFE and autologous vein and the surface has been seeded with endothelial cells or otherwise treated. Each of these solutions suffer from certain drawbacks, such as not being biocompatible, lacking sufficient mechanical strength, having a surface that is difficult to prepare, lack of ready availability and being thrombogenic.
Antithrombotic drug regimens, in which anticoagulants and thrombolytic agents are administered during and after deployment of the stent, have also been employed to reduce the risk of thrombosis.
In the art it is known to cover stents with jackets made of serous membrane.
Serous membrane is a type of tissue that holds various organs together and include the peritoneum (the serous membrane that lines the cavity of the abdomen of a mammal and is folded inward over the abdominal and pelvic viscera), the pericardium (the conical sac of serous membrane that encloses the heart and the roots of the great blood vessels) and the pleura (the serous membrane that lines each half of the thorax and is folded back over the surface of the lung of the same side). The serous membranes release a lubricating serous fluid allowing the expanding and contracting organs (including the lungs) held within a given serous membrane to slide gently against adjacent parts of the body.
Serous membranes are made of two strata of tissue. The serous stratum or layer of a serous membrane is a very smooth single layer of flattened, nucleated mesothelial cells united at their edges by cement substance. The serous layer is the side that faces towards and contacts the organs. The serous cells secrete the lubricating serous fluid. The serous cells rest on a basement layer or stratum (also called the subserous areolar tissue), a rough, strong fibrous layer that forms a protective sack about the serous layer. Beneath the basement membrane are networks of yellow elastic and white fibers imbedded in ground substance that also contains connective-tissue cells.
The use of serous membranes as a component of intracorporeal implants is known in the art.
In U.S. Pat. No. 4,502,159 is taught a method for preparing a tubular graft from pericardium.
In U.S. Pat. No. 5,782,914 is taught a method for processing animal tissue such as serous membranes for use as a graft material in intracorporeal implants.
In U.S. Pat. No. 5,934,283 is taught the use of tissues, including serous tissues such as pericardium, peritoneum and tunica vaginalis in fashioning a pubovaginal sling.
In U.S. Pat. No. 5,865,723 and in PCT Patent Application No. PCT/US96/20868 published as WO 97/24081 is discussed that vascular prostheses of autologous pericardial membrane fashioned into tubular grafts have been used but have been proven to be ineffective, for example as the pericardial membrane is subject to rupture and structural failure. Therefore in WO 97/24081 is taught a stent assembly comprising pericardial, fascial rectus sheath or venous tissue formed as a jacket over a stent. The tissue is harvested, usually but not necessarily treated in a stabilizing medium, and attached to the outside of the stent by rolling over the stent so that the two edges of the tissue overlap by at least 35° (and preferably are wrapped twice about the stent) so as to obviate the need for sutures.
Due to the overlapping layers of pericardium, stent assemblies jacketed in accordance with the teachings of WO 97/24081 are quite thick, causing a significant reduction in the bore size of a bodily vessel in which deployed, limiting such stent assemblies for deployment only to relatively large bore lumina. Further, the thickness of a stent jacket made in accordance with the teachings of WO 97/24081 reduces the flexibility and consequently maneuverability of such a stent assembly, limiting the locations in which such stents can be deployed.
In PCT Patent Application No. PCT/US96/13907 published as WO 97/09006 is taught a stent assembly comprising a jacket of at least one layer of pericardial tissue (preferably human, bovine or porcine origin) covering at least a portion of the inside or outside surface of a stent. The thickness of the jacket is adjusted by varying the number of layers of pericardium. The disadvantages of such stent assemblies are similar to those of WO 97/24081.
Thus, there is a need for a stent capable of minimizing restenosis while having a consistency similar to the native artery, a non-thrombogenic surface and sufficient mechanical strength as well as being biocompatible and readily available.
It would be highly advantageous to have a material for use as a component in intracorporeal implants such as stents not having at least some of the disadvantages of the prior art.